FIG. 1 illustrates a conventional battery management module 100. In the battery management module 100, if the battery voltage of the battery 102 is in a normal operation range, the battery management unit (BMU) 104 can turn on the charge switch NCHG to pass a normal charging current ICHG to charge the battery 102. If the battery voltage is below the normal operation range, e.g., the battery 102 is over-drained, then the BMU 102 turns on the pre-charge switch PCHG to pass a pre-charge current IPCHG, e.g., trickle current, to charge the battery 102. The pre-charge resistor RPCHG coupled to the pre-charge switch PCHG has relatively high resistance to control the pre-charge current IPCHG to be relatively small, so as to protect the over-drained battery 102.
The battery management module 100 has some shortcomings. For example, the pre-charge current IPCHG can be given by: IPCHG=(VPACK+−VBATT)/RPCHG, where VPACK+ represents a voltage at the input terminal PACK+, and VBATT represents a voltage at the positive terminal of the battery 102. Thus, the pre-charge current IPCHG decreases if the battery voltage VBATT increases, and this slows down the pre-charging process. In addition, the pre-charge resistor RPCHG consumes additional power when the pre-charge current IPCHG flows therethrough. Moreover, the pre-charge resistor RPCHG and switch PCHG are high-power elements capable of sustaining a high voltage difference between the input voltage VPACK+ and the battery voltage VBATT, and therefore they are relatively expensive and increase the cost of the battery management module 100. Furthermore, the pre-charge resistor RPCHG and switch PCHG increase the PCB size for the battery management module 100.
A battery management module that addresses the abovementioned shortcomings would be beneficial.